High frequency devices, circuits and subsystems, such as those operating at radio frequency (RF) and microwave frequency ranges, are often manufactured as or using a planar circuit. The planar circuits, typically referred to as ‘printed circuit boards’ (PCBs), frequently are interconnected with one another using coaxial cables. Coaxial connectors at an interface between a PCB and the coaxial cable enable the individual PCB to be connected and disconnected during assembly and/or test, as well as for maintenance and replacement purposes once the PCB has been deployed. A variety of classes or series of standard and semi-custom coaxial connectors are readily available and in widespread use including, but not limited to, SMA, SMB, SMC, SSMA, 3.5-mm, and 2.4-mm, 1.85-mm connectors. In general, each of the various coaxial connector series is available in a variety of styles, each style being adapted to a particular application and/or circuit-mounting configuration.
Among the coaxial connector styles used in conjunction with high frequency PCBs are surface-mountable styles often referred to as ‘surface mount’ (SMT) connectors. FIG. 1A illustrates a perspective view of a typical, conventional SMT coaxial connector 10 that emphasizes an end (hereinafter the end view is referred to as being ‘top-oriented’). FIG. 1B illustrates a perspective view of the SMT connector 10 of FIG. 1A that emphasizes an opposite end (hereinafter the opposite end view is referred to as being ‘bottom-oriented’). FIG. 2 illustrates a cross sectional view of the conventional SMT connector 10 of FIG. 1A attached to a PCB 11, the connector 10 being interfaced with a microstrip transmission line 24 on the PCB 11.
The conventional SMT connector 10 illustrated in FIGS. 1A, 1B and 2 comprises a connector shell or barrel 12, a connector base 14, a center pin 16, and a dielectric pin support 18. The base 14, connected to a first end 12a of the shell 12, comprises a flange 20 and a plurality of spacer legs or stand-offs 22. The center pin 16 is mounted in and extends a length of a through hole of the shell 12. The shell through hole runs axially through the shell 12 and through the flange 20 from a second or connector end 12b of the shell 12 to an outer surface 19 of the flange 20. The center pin 16 is supported in the through hole by the dielectric pin support 18. Together, the through hole through the shell 12 and the flange 20 along with the center pin 16 therethrough form a coaxial transmission line. The center pin 16 extends axially beyond the outer surface 19 of the flange 20 a distance equivalent to a length of the spacer legs 22. Typically, the connector 10 is interfaced to the PCB 11 by soldering a connection end 16a of the center pin 16 to a transmission line 24 of the PCB 11 and soldering or otherwise electrically connecting the spacer legs 22 to a ground plane 28 of the PCB 11.
The presence of the spacer legs 22 creates a gap 30 between the outer surface 19 of the flange 20 and a top surface of the PCB 1. The gap 30 enables a solder joint 26 at the connection end 16a of the center pin 16 to be cleaned and inspected during manufacturing. In addition, the gap 30 insures that expansion of the dielectric pin support 18 during solder reflow will not interfere with proper solder attachment of the center pin 16. In particular, the gap 30 accommodates any expansion of the dielectric pin support 18 such that the connector 10 does not lift off of the PCB 11 surface during soldering.
Unfortunately, the presence of the gap 30 results in a signal path discontinuity experienced by a signal traveling between the connector 10 and the transmission line 24 of the PCB 11. In particular, the signal path discontinuity exists in the SMT connector 10 transmission line between the outer surface 19 of the flange 20 and the PCB 11 surface where the center pin 16 is attached to the transmission line 24 of the PCB 11. In addition, a solder joint or fillet 26 formed when the center pin 16 is soldered to the transmission line 24 tends to exacerbate the discontinuity associated with the gap 30.
Ultimately, the discontinuity associated with the gap 30 and solder fillet 26 leads to unwanted or spurious electromagnetic radiation (EM) from the interface between the connector 10 and the PCB 11. In addition, the discontinuity associated with the gap 30 and solder fillet 26 manifests itself as an impedance mismatch, thereby introducing unwanted signal reflections in the signal path passing through the connector 10 and to the PCB 11. The signal reflections can and often do interfere with a performance of a device or system that employs conventional SMT connectors.
Accordingly, it would be advantageous to have an SMT connector that minimized spurious EM radiation and minimized a signal path discontinuity and associated impedance mismatch associated with interfacing the SMT connector to a PCB. Such a coaxial connector would address a longstanding need in the area of surface-mountable connectors for RF and microwave applications.